It has been 15 years since Timothy McVeigh detonated a massive truck bomb at the Oklahoma City federal building, destroying it and killing 168 innocent people, including 19 children under age six.

As part of the team that prosecuted McVeigh and his co-conspirator, Terry Nichols, it was clear to me that both terrorists were motivated by hatred and fear of what they saw as an over-reaching federal government.

While McVeigh and Nichols were not part of any larger organization, their political grudges were nurtured and reinforced by the toxic ideology of the "patriot" movement of the early Clinton years.

This movement, which found expression at gun shows and in militia groups, gained traction after Bill Clinton's election in 1992, and the disastrous siege at Waco in 1993. But it really took off when Congress passed a ban on assault rifles in 1994. The movement viewed this as the first step in a government plan to strip Americans of their right to bear arms.

This vitriol was fanned by incendiary sentiments from relatively mainstream figures on the right. They explicitly encouraged nutty theories about Clinton and his administration, including crackpot theories blaming him for the "murder" of Vincent Foster.

There are striking similarities between the tenor of that political discourse and today.

Again, we have a relatively liberal president who is despised and feared by the far right. Again, we have controversial legislation described in apocalyptic terms by some mainstream conservatives.

While the assault weapons ban was viewed as the vanguard of a government effort to take guns from law-abiding citizens, the health reform bill is depicted as the first step in government takeover of health care and the descent into Soviet-style totalitarianism.

Shortly before the Oklahoma City bombing, the National Rifle Association vice president, Wayne LaPierre, sent a fund-raising letter describing federal law agents as "Jack-booted thugs" who wear "Nazi bucket helmets and black storm trooper uniforms." To his credit, former President George H.W. Bush resigned from the NRA soon after.

McVeigh was a devoted believer that a small, committed group of freedom-loving Americans could and should instigate a revolution against an oppressive federal government that threatened their right to carry guns.

He intended his Oklahoma City bombing to be the first shot in a second American revolution, of which he would be remembered as the founding father.

Not surprisingly, his plan failed miserably. His crime stands not as the spark that lit a powder keg of anti-government resentment, but as an isolated and senseless act.

One can, of course, be a vociferous critic of the administration's approach to health reform without fomenting violent resistance. Certainly, most Republicans and conservative commentators have made clear that the only "revolution" they favor is at the ballot box.

But we have begun to see talk of violence and revolution creeping into mainstream discourse.

We've heard a governor speak of secession, we've seen revolutionary signs at rallies for a likely GOP presidential candidate and we've listened to well-respected leaders accuse colleagues of "shredding" the Constitution.

History tells an unfortunate story about can happen next. When extreme rhetoric and hyperbole are used by mainstream figures, impressionable actors on the political fringe can take this seriously.

If you believe the hyperbole, taking violent action doesn't seem so crazy. In fact, it's the logical reaction.

After all, if you believe legal abortions really are tantamount to a continuing "Holocaust," as is claimed by well-known national organizations, then attacks on ob-gyn providers who perform abortions can look justified.

Of course, despicable individuals like McVeigh must bear responsibility for their own actions. We cannot transfer blame to those who merely spew violent, hateful or inflammatory rhetoric.

It is true that mere talkers have no legal responsibility when an impressionable, perhaps unbalanced, person decides to act on their vitriol.

But those who say their words are only words, or say their hyperbole is justified to make their message heard, cannot pretend that they play no role in inciting the actions that follow.

We protect free speech. Yet that does not mean those whose speech precedes bloodshed are free from blame.

Aitan Goelman, a partner with a Washington law firm, served as a federal prosecutor in the Oklahoma City bombing.